Intervertebral implant

ABSTRACT

In an intervertebral implant, having an upper part that has a support face for a vertebra and a lower part that has a support face for an adjacent vertebra, on each of which parts engagement elements, which are accessible from one side of the intervertebral implant, for a manipulation instrument are disposed, in order to minimize the structural height of the intervertebral implant upon insertion into an intervertebral space, it is proposed that the upper part and lower part each have protrusions and recesses aimed at the respectively other part, which are offset laterally from one another in such a way that when the upper part has been brought close to the lower part they mesh with one another; and that the engagement elements on the upper part and on the lower part are each disposed in protrusions of these parts in such a way that the engagement elements of the upper part and lower part are located side by side and at least partly overlap in the direction of the height of the intervertebral implant.

This application is a continuation of U.S. application Ser. No.10/018,402, filed Jun. 12, 2002 now U.S. Pat. No. 6,936,071, which was aU.S. national stage application based on international application Ser.No. PCT/EP99/04628, filed Jul. 2, 1999.

BACKGROUND OF THE INVENTION

The invention relates to an intervertebral implant, having an upper partthat has a support face for a vertebra and a lower part that has asupport face for an adjacent vertebra, on each of which parts engagementelements, which are accessible from one side of the intervertebralimplant, for a manipulation instrument are disposed, in order tominimize the structural height of the intervertebral implant uponinsertion into an intervertebral space.

One such intervertebral implant is known for instance from U.S. Pat. No.5,314,477. This intervertebral implant is used to replace a disk removedfrom the intervertebral space, and accordingly the intervertebralimplant must have a relatively low structural height, since it has tofit into the gap between vertebrae. This is particularly difficult if anadditional pivot insert is also embedded between the upper part and thelower part, as is the case in the known intervertebral implant of U.S.Pat. No. 5,314,477.

But even in two-piece intervertebral implants, difficulties also arise,especially if the implants also have pins and other protrusions on theirsupport faces that are intended for anchoring the intervertebral implantin the bone. Often, these parts can be inserted only by widening theintervertebral space greatly. Not only is this difficult, but it alsopresents the risk of injuries.

Since the intervertebral space has a relatively low height, it is alsodifficult for engagement elements that a manipulation instrument canengage to be secured to both parts of the intervertebral implant. It isconventional to have such manipulation instruments engage the upper partand the lower part separately, for instance by means of pins that areinserted into bores on the upper part and lower part, so that with themanipulation instrument, the two parts of the intervertebral implant canbe inserted into the intervertebral space and can optionally also bevaried in terms of their spacing from one another, thereby allowing acertain spreading open of the intervertebral space. In this respect,reference is made to the pincerlike manipulation instrument of U.S. Pat.No. 5,314,477.

Because of the strong forces, it is necessary to provide a certainstructural height for the engagement elements; for instance, thereceiving bores must have a certain diameter. This dictates a minimumstructural height for the upper part and for the lower part, and inconventional intervertebral implants, the structural heights of theupper part and lower part are thus added together, so that even if theupper and lower parts rest directly on one another, a relatively greatstructural height of the intervertebral implant is still unavoidable.

SUMMARY OF THE INVENTION

It is the object of the invention to embody an intervertebral implant ofthis generic type in such a way that the minimum structural height isreduced, to make it easier to insert the intervertebral implant into theintervertebral space.

In an intervertebral implant of the type described at the outset, thisobject is attained in accordance with the invention in that it isproposed that the upper part and lower part each have protrusions andrecesses aimed at the respectively other part, which are offsetlaterally from one another in such a way that when the upper part hasbeen brought close to the lower part they mesh with one another; andthat the engagement elements on the upper part and on the lower part areeach disposed in protrusions of these parts in such a way that theengagement elements of the upper part and lower part are located side byside and at least partly overlap in the direction of the height of theintervertebral implant.

In such an embodiment, a minimal structural height of the twointervertebral implant parts resting on one another can be attained,since the engagement elements, which cannot fall below a minimalstructural height, are each disposed in protrusions of the upper partand lower part, or in other words in the parts of the upper part andlower part that have the greatest structural height. These regions ofgreat structural height are embodied as protrusions, next to which arerespective recesses, into which the protrusions of the respectivelyother part can dip. As a result, on the one hand, the engagementelements for the manipulation instruments are located side by side, andon the other, they can at least partly overlap, so that the totalstructural height of the parts resting on one another of theintervertebral implant can be reduced markedly compared to conventionalintervertebral implants. The result is accordingly an internestedarrangement of the upper and lower parts, with maximal exploitation ofthe available material height.

It is favorable if the engagement elements are insertion openings forpinlike retaining elements of a manipulation instrument; because of thedescribed construction, these insertion openings can have a relativelylarge diameter and can thus receive strong retaining pins, andnevertheless a relatively low structural height of the intervertebralimplant with parts resting directly on one another is obtained.

It is advantageous if the insertion openings extend substantiallyparallel to the support faces; once again, this prevents an increase inthe structural height of the intervertebral implant parts.

In a preferred embodiment, it is provided that the lower part has acentral indentation, opposite the lower support face, which indentationis surrounded by a U-shaped edge. Thus with the lower part and upperpart resting directly on one another, the indentation serves to receivea protrusion on the upper part.

It is advantageous if the upper part has a central protrusion that fitssubstantially in complimentary fashion into the indentation; that is,the total volume of the indentation is utilized for the protrusion.

It is also advantageous if the engagement elements of the lower part aredisposed on the two ends of the U-shaped edge, or in other words arelocated on the outside.

Conversely, the engagement elements of the upper part can be disposed onthe central protrusion of the upper part, or in other words are locatedfarther inward than the engagement elements of the upper part.

In particular, the engagement elements of the upper part can be disposednear the lateral edges of the central protrusion, so that for the upperpart as well, the spacing of the engagement elements can be selected tobe relatively great; as a result, both the upper part and the lower partcan be reliably secured against skewing.

It should already be noted here that the words “lower part” and “upperpart” do not necessarily say anything about the installed position ofthe intervertebral implant in the spinal column; the part called the“lower part” could in fact be above in the spinal column. Therefore,these parts may also be referred to as first and second parts havingouter and inner surfaces. What is essential is merely that the upperpart and lower part define the intervertebral implant on opposite sidesof the implant.

It is especially advantageous if the upper part and/or the lower part isembodied in substantially platelike fashion; these parts naturally, inaccordance with the design of the invention, have protrusions andrecesses that are oriented toward the respectively other part. Theplatelike embodiment, however, leads as a whole to a very low structuralheight of the intervertebral implant.

In a preferred embodiment, the lower part and the upper part each have arespective receptacle for a pivot insert. This pivot insert, which isplaced between the upper part and lower part after the insertion of theintervertebral implant, supports the upper part and lower part againstone another; it takes on a resilient function, for instance, andfurthermore leads to a certain pivotability of the two parts of anintervertebral implant relative to one another, so that a pivotabilityof the adjacent vertebra is thus attainable as well.

In particular, it is advantageous if the pivot insert has at least onespherical support face, which engages the correspondingly sphericallyshaped receptacle.

It is favorable if the spherical receptacle is disposed in the centralprotrusion of the upper part.

It is also advantageous if the central indentation of the lower partforms the receptacle for the pivot insert.

According to a preferred embodiment of the invention, it is providedthat the pivot insert can be inserted from the side into the receptacle,which has the engagement elements for a manipulation instrument. This isthe side from which the upper part and lower part are introduced intothe intervertebral space, and it is also from this side that the pivotinsert can then be thrust between the already-inserted parts of theintervertebral implant.

It is favorable if the pivot insert is insertable into the receptaclealong a guide.

In that the insert as well is preferably embodied substantially inplatelike fashion.

An especially favorable design is obtained if the insert substantiallycompletely fills up the central receptacle and with its sphericalsupport face protrudes from the receptacle.

BRIEF DESCRIPTION OF THE DRAWINGS

The ensuing description of preferred embodiments of the invention servesin conjunction with the drawing to provide further explanation. Shownare:

FIG. 1: a perspective exploded view of an intervertebral implant with anupper part, a lower part, and a pivot insert that can be insertedbetween them;

FIG. 2: a perspective exploded view of the upper part and the lower partof the intervertebral implant, without an inserted pivot insert;

FIG. 3: a view similar to FIG. 2 with the pivot insert inserted into thelower part;

FIG. 4: a perspective view of the upper part and the lower part of theintervertebral implant with maximum mutual proximity;

FIG. 5: a front view of the intervertebral implant of FIG. 4;

FIG. 6: a perspective view of the intervertebral implant with the pivotinsert inserted; and

FIG. 7: a cross-sectional view of the intervertebral implant of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The intervertebral implant 1 shown in the drawing includes three parts,namely a platelike upper part 2, a platelike lower part 3, and asubstantially platelike pivot insert 4. In plan view, the implant,although having rounded corners, is generally rectangular.

The upper part 2 is embodied flat on its top, thus creating a supportface 5, on which various kinds of protrusions 6, 7 are disposed whichserve the purpose of anchoring the upper part 2 in a vertebra thatrests, with its end face toward an intervertebral space, on the supportface 5.

The upper part 2 is substantially rectangular in cross section; in theexemplary embodiment shown, a longitudinal edge 8 curves outward.

On the two short sides of this rectangle, the thickness of the platelikeupper part 2 is less than in the central region, so that along the shortsides of the upper part 2, downward-pointing recesses 9 each extendingparallel to these edges are formed that are open toward the outside. Thecentral region of the upper part 2 is located between the two recesses 9and thus has a greater thickness or height and thus forms adownward-pointing protrusion 10 embodied between the two recesses 9.This protrusion is defined by an underside 11, which extendssubstantially parallel to the support face 5 and in which there is aspherical indentation 12, which forms a bearing plate for the pivotinsert 4.

The lower part 3 of the intervertebral implant 1 is also platelike inembodiment and on its underside has a flat support face 13 withprotrusions 14 and 15, which correspond to the protrusions 6 and 7 ofthe support face 5. On the side remote from the support face 13, thethickness of the lower part 3 is less in the central region than in anouter region. This outer region of greater thickness has the form of aU, with two parallel legs 16, 17, which extend parallel to the shortedges of the lower part 3, which in cross section is embodied similarlyto the upper part 2, and with a crosspiece 18 that connects the two legs16 and 17 on one end. The region enclosed by the legs 16 and 17 and thecrosspiece 18 forms a central indentation 19, whose area issubstantially equivalent to the area of the central protrusion 10 of theupper part 2, while the disposition and length of the legs 16 and 17correspond essentially to the disposition and length of the recesses 9on the upper part 2. As a result, it is possible to place the upper 2and lower part 3 on one another in such a way that the centralprotrusion 10 of the upper 2 dips into the central indentation 19, whilethe legs 16 and 17 of the lower part 3 dip into the recesses 9 of theupper part 2 (FIG. 4); in this position, the upper part 2 and lower part3 have maximum proximity to one another and a minimal structural height.

The dimensions are selected such that the various recesses areessentially filled completely by the protrusions dipping into them.

Blind bores 20 and 21 are machined into the two legs 16 and 17 of thelower part 3, extending parallel to these legs 16, 17 from their freeends; the diameter of these bores is relatively great in proportion tothe height of the legs 16, 17, and this diameter is in fact greater thanthe thickness or height of the lower part 3 in the region of the centralindentation 19.

Blind bores 22 and 23, which extend parallel to the blind bores 20 and21 in the lower part 3, are machined into the central protrusion 10 ofthe upper part 2, in the vicinity of its side edges. These blind bores22 and 23 again have a relatively great diameter, which corresponds to asubstantial portion of the height of the protrusion 10 and is greaterthan the thickness of the upper part 2 in the region of the recesses 9.

When the upper part 2 and lower part 3 rest tightly against one anotherin the manner described, the blind bores 20 and 21 of the lower part 3and the blind bores 22 and 23 of the upper part 2 overlap at leastpartly in the direction of the height of the intervertebral implant 1,as is clearly shown in FIGS. 4 and 5.

The blind bores 20, 21, 22 and 23 serve as receptacles for pinlikeextensions of a manipulation instrument, not shown in the drawing, andthus form engagement elements for this manipulation instrument, which inthis way separately engages the upper part 2 and the lower part 3. Withthis manipulation instrument, it is possible to introduce the upper part2 and the lower part 3 of the intervertebral implant 1 into anintervertebral space; the very low structural height of theintervertebral implant 1 facilitates this introduction, which can bedone essentially without major widening of the intervertebral space.

After the introduction of the upper part 2 and lower part 3 in this way,the two parts of the intervertebral implant 1 can be spread apart; thatis, their spacing is increased, for instance with the aid of themanipulation instrument that is holding the upper part 2 and the lowerpart 3. Thus, in accordance with the method of operation, the upper andlower parts 2, 3 (or the first and second parts) are first insertedtogether into the intervertebral space, after which these parts 2, 3 areseparated from each other and the insert is inserted between them.Thereafter, these parts 2, 3 are allowed to come together towards eachother to engage the insert.

In this spread-open position of the upper part 2 and lower part 3, it ispossible to thrust the pivot insert 4 between the upper part 2 and thelower part 3.

This pivot insert is constructed essentially in the shape of a plate,which has a flat underside 24 and a spherically upward-curved top side25. The outer dimensions of the platelike pivot insert correspond tothose of the central indentation 19 in the lower part 3, so that thepivot insert 4 can be thrust into this indentation, filling it up,specifically from the side toward which the blind bores 20, 21, 22, 23open. Guide strips 26 on the side edges of the pivot insert 4 engagecorresponding guide grooves 27 in the legs 16, 17, so that an insertionguide for the pivot insert 4 is formed that fixes it in the lower part 3after its insertion. The inserted pivot insert 4, after insertion, fillsup the indentation 19 and protrudes with its spherically curved top side25 upward past the top side of the lower part 3; the spherical top side25 dips in complimentary fashion into the spherically curved indentation12 on the underside of the protrusion 10, where with the upper part 2 itforms a ball joint, which enables a certain pivotability of the upperpart 2 relative to the lower part 3 (FIG. 7).

The pivot insert 4 can have a detent protrusion 28 on its flat underside24; when the pivot insert 4 is inserted into the lower part 3, thisprotrusion locks elastically into a detent recess 29 that is located onthe bottom of the indentation 19; as a result, the pivot insert 4 isalso fixed in the insertion direction in the indentation 19.

The upper part 2 and lower part 3 are preferably made of physiologicallysafe metal, such as titanium, while the pivot insert 4 preferablycomprises a likewise physiologically safe plastic material, such aspolyethylene. These support faces 5 and 13 can be embodied in anespecially bone-compatible way; for instance, this surface can beroughened by a coating, so that optimal anchoring to the adjacent bonematerial is obtained.

The invention may also be described as follows, which description is thefull equivalent of the preceding discussion. An upper part 2 has anupper surface 5 for engaging a vertebrae and a lower surface whichcomprises a downward pointing protrusion 10 between side recesses 9 anda rounded portion, preferably in the form of a concave sphericalindentation 12. A lower part 3 has a lower surface 13 for engaging avertebrae. A pivot insert 4, when joined to the lower part 3, as shownfor example in FIG. 3, provides a convex upper surface portion 25,preferably spherical, in operational engagement with the rounded portion12 of the upper part.

The lower part 3 and pivot insert 4 may, taken together, be described asa lower part formed in two pieces, namely the elements 3 and 4, whereinthe element 3 may be referred to as a lower piece and the element 4 maybe referred to as an upper piece.

The upper and lower parts include on their upper surface and lowersurface, respectively, protrusions 6 and 14 which may also be referredto as anchors, which anchor the upper and lower parts, respectively,into the adjacent vertebrae that form the intervertebral space and restagainst the respective upper and lower surfaces.

As shown in the figures, the anchors 6 and 14 are each single anchors,preferably extending perpendicular to the respective outer surfaces fromwhich they extend. The anchors may also be referred to as anchorportions and the plane or line along which the anchor or anchor portionsextend may be referred to as an anchor line. Each of the anchors 6 and14 has a zigzag edge which comprises a series of teeth. As shown at thecross-sectional view of FIG. 7, anchor 6 is greater in height than theremainder of the upper part 2, i.e., from surface 5 to the bottom ofprotrusion 10, at the section of the upper part where the anchor sectionmeets the surface of the part. Similarly, at that cross-section theanchor 14 is greater in height than the remainder of the lower part 3exclusive of its convex portion, i.e., from lower surface 13 to the topof walls 16, 17 and 18. As can be seen from the perspective view ofthese same parts shown in FIG. 6, anchor 6 is aligned along a singleanchor line across surface 5 to form a single anchor plane, this anchorplane having an anchor plane height which is greater than the height ofthe remainder of the upper part 2 at the section of the upper part wherethe anchor plane portion meets the surface. Alternatively, oradditionally, as best shown in the front view of the parts depicted inFIG. 5, the anchor 6 is at least substantially equal in height to theoverall height of the remainder of the upper part 2, i.e., from surface5 to the bottom of protrusion 10 with its longitudinal edge 8. As alsoshown in the figures, in the preferred embodiment, the length of theanchors 6 and 14, i.e., in the direction from the anterior to theposterior thereof, is greater than one half of the overall dimension ofits respective part from its anterior to its posterior (as defined withreference to the part's anterior posterior orientation in the body uponimplantation), passing through that anchor. As also noted in thefigures, the vertical height of each anchor 6 and 14 is greater than itswidth which is the dimension taken horizontally in FIG. 5 or 7.Furthermore, in the illustrated embodiment as shown in FIGS. 5 and 7 theanchors 6 and 14 lie essentially in a common vertical plane in theassembled implant. As best shown in FIG. 7, pivot insert 4 enables acertain pivotability, or articulating motion, of the upper part 2relative to the lower part 3. Midlines are line on the outer surfacespassing essentially through the center of the outer surfaces of parts 2and 3. Such midlines may divide the part into two separate halves. Inthe illustrated embodiment, the common vertical plane of anchors 6 and14 is located essentially at a midline of the implant which lies in ananterior to posterior plane of the implant, again as defined withreference to the intended orientation of the implant upon implantation.Each anchor 6 and 14 is elongated along the anterior to posteriormidline and the width of each anchor straddles the midline.

The lower part comprises three walls including parallel side walls 16and 17 and a rear wall 18. These walls form between them a centralindentation 19 which comprises a recess with a generally flat surface.The fourth side of the recess is open. The pivot insert 4 has a detent28 that snap-fits into a detent recess 29 formed in the generally flatsurface of recess 19.

As best shown in FIGS. 2, 4 and 5, in the absence of pivot insert 4, theprotrusion 10 of upper part 2 can fit down between walls 16, 17 and 18of the lower part 2. This fitting of protrusion 10 within the recess 19,surrounded by walls 16, 17 and 18 may be referred to as “nesting” sincethe protrusion 10 essentially “nests” within recess 19. With the upperand lower parts in this nested condition, as shown in FIGS. 4 and 5, thecombined height of the upper and lower parts 2 and 3, i.e., the heightfrom surface 13 to surface 5, is less than the total additive height ofthe upper and lower parts, taken separately, i.e., less than the totalof the height from surface 13 to the top of walls 16, 17 and 18 plus theheight from surface 5 to the bottom of protrusion 10.

To reach its final destination within an intervertebral space, theimplant must of course be moved along a path, i.e., an insertiondirection from outside of the patient, into the patient, and then intothe inververtebral space. In the illustrated embodiment, as describedabove, instruments would engage apertures 20, 21, 22 and 23 to moveimplant along a path in an insertion direction. The anchors 6 and 14 areparallel to this path and each defines a single anchor line parallel tothis path as the implant is moved into an intervertebral space. Eachanchor is thus adapted to enter a groove in the adjacent vertebra as theimplant is inserted. As a point of reference, lateral planes parallel tothe direction of this path pass through the outermost boundaries of theimplant, which, in the preferred embodiment, would be the opposed sidesurfaces of the parts. Each anchor 6 and 14 lies at a midline at thecenter of the outer surface of each part 2 and 3 in between and parallelto the lateral parallel planes. Thus, in the illustrated embodiment, thepath would be parallel to the front to rear (anterior to posterior)direction, wherein, during insertion, the rear (posterior) of theimplant would constitute the lead end and the front (anterior) thereofwould constitute the trailing end.

Although the invention has been described in detail with respect topreferred embodiments thereof, it will be apparent that the invention iscapable of numerous modifications and variations, apparent to thoseskilled in the art, without departing from the spirit and scope of theinvention.

The invention claimed is:
 1. An intervertebral implant that isconfigured to be retained within an intervertebral disc space betweenadjacent first and second vertebrae, comprising: a first part having afirst outer surface adapted for engaging the first vertebra, a firstinner surface opposing and facing away from the first outer surfacehaving a concave indentation, and a first sidewall located between thefirst outer and inner surfaces extending around the circumference of thefirst part; a second part having a second outer surface adapted forengaging the second vertebra, a second inner surface opposing and facingaway from the second outer surface having a convex protrusion portionadapted to engage the indentation of the first part, and a secondsidewall located between the second outer and inner surfaces extendingaround the circumference of the second part, wherein on the second innersurface, located between the convex portion and the second sidewall andlocated radially outward of the convex portion, there is a portion notadapted to engage the indentation of the first part; wherein at leastone of the first part concave indentation and the second part convexportion is a spherical surface; wherein the first part and the secondpart each have a leading end and a trailing end opposite the leadingend, and opposing lateral sides between the leading end and the trailingend; wherein the first and second parts each have an elongated anchorthat is elongated in a lengthwise direction from the trailing end to theleading end and having a height greater than its width on theirrespective first and second outer surfaces, and extending outwardly fromthe respective outer surfaces, each elongated anchor being locatedessentially along the center of the respective first and second outersurfaces between the lateral sides, the first and second part anchorsbeing adapted to anchor the respective part in the respective vertebra;and wherein the first and second parts can be engaged in an insertionposition with the respective leading ends forward and the lateral sidesof the first part generally parallel with the lateral sides of thesecond part such that the elongated anchors lie in essentially the samevertical plane and wherein the first and second parts are adapted suchthat in the insertion position with the elongated anchors verticallyoriented in the direction of the respective anchor height, the firstsidewall is located in a different horizontal plane than the secondsidewall.
 2. The intervertebral implant of claim 1 wherein the firstpart anchor is the only anchor of the first part having a height greaterthan the height of the remainder of the first part.
 3. Theintervertebral implant of claim 2 wherein the maximum height of thefirst part anchor is greater than the maximum height of the firstsidewall.
 4. The intervertebral implant of claim 2 wherein the maximumheight of the second part anchor is greater than the maximum height ofthe second sidewall.
 5. The intervertebral implant of claim 3 whereinthe maximum height of the second part anchor is greater than the maximumheight of the second sidewall.
 6. The intervertebral implant of claim 1wherein the maximum height of the first part anchor is greater than themaximum height of the first sidewall.
 7. The intervertebral implant ofclaim 6 wherein the maximum height of the second part anchor is greaterthan the maximum height of the second sidewall.
 8. An intervertebralimplant configured to be inserted into an intervertebral space betweenadjacent first and second vertebrae, comprising: a first platelike parthaving a substantially flat first outer surface adapted for engaging thefirst vertebra, a first inner surface opposing and facing away from thefirst outer surface having a concave indentation, and a first sidewalllocated between the first outer and inner surfaces extending around thecircumference of the first part; a second platelike part having asubstantially flat second outer surface adapted for engaging the secondvertebra, a second inner surface opposing and facing away from thesecond outer surface having a convex portion adapted to engage theindentation of the first part, and a second sidewall located between thesecond outer and inner surfaces extending around the circumference ofthe second part, wherein on the second inner surface, located betweenthe convex portion and the second sidewall and located radially outwardof the convex portion, there is a portion not adapted to engage theindentation of the first part; wherein at least one of the first partconcave indentation and the second part convex portion is a sphericalsurface; wherein the first part and the second part each have a leadingend and a trailing end opposite the leading end, and opposing lateralsides between the leading end and the trailing end; wherein the firstand second parts each have an anchor midline on their respective firstand second outer surfaces extending in the direction from the trailingend to the leading end passing essentially through the center of thefirst and second outer surfaces between the lateral sides; a firstelongated anchor extending outwardly away from the first outer surfaceessentially along the anchor midline and where the first anchor iselongated in the direction of the anchor midline, the first anchor beingadapted to anchor the first part in the first vertebra; and a secondelongated anchor extending outwardly away from the second outer surfaceessentially along the anchor midline and where the second anchor iselongated in the direction of the anchor midline, the second anchorbeing adapted to anchor the second part in the second vertebra; whereinthe first and second parts can be engaged in an insertion position withthe respective leading ends forward and the lateral sides of the firstpart generally parallel with the lateral sides of the second part suchthat the elongated anchors lie in essentially the same vertical plane;wherein each of the first and second anchors has a height greater thanits width, and wherein when the implant is adapted to be configured inthe insertion position with the elongated anchors vertically oriented inthe direction of the respective anchor height, the first sidewall islocated in a different horizontal plane than the second sidewall.
 9. Anintervertebral implant according to claim 8, wherein the first andsecond parts are, in plan view, generally rectangular in shape.
 10. Anintervertebral implant according to claim 8 wherein the maximum heightof the first anchor is greater than the maximum height of the firstsidewall.
 11. An intervertebral implant according to claim 10 whereinthe maximum height of the second anchor is greater than the maximumheight of the second sidewall.
 12. An intervertebral implant accordingto claim 8 wherein the maximum height of the second anchor is greaterthan the maximum height of the second sidewall.
 13. An intervertebralimplant according to claim 8, wherein the first anchor is the onlyanchor of the first part having a height greater than the height of theremainder of the first part.
 14. An intervertebral implant according toclaim 13, wherein the first and second parts are adapted for engagementsuch that the first and second anchors are essentially coplanar andvertically aligned with each other, and wherein the first and secondanchors are adapted to be anchored in respective grooves in the firstand second vertebrae.
 15. An intervertebral implant according to claim13 wherein the maximum height of the first anchor is greater than themaximum height of the first sidewall.
 16. An intervertebral implantaccording to claim 15 wherein the maximum height of the second anchor isgreater than the maximum height of the second sidewall.
 17. Anintervertebral implant according to claim 13 wherein the maximum heightof the second anchor is greater than the maximum height of the secondsidewall.
 18. An intervertebral implant according to claim 8 wherein thefirst and second parts are adapted for engagement such that the firstand second anchors are essentially coplanar and vertically aligned witheach other, and wherein the first and second anchors are adapted to beanchored in respective grooves in the first and second vertebrae.
 19. Anintervertebral implant according to claim 18, wherein the first andsecond parts are adapted to be operatively engaged to allow pivotabilityof said first part relative to said second part.
 20. An intervertebralimplant according to claim 18, wherein the first and second parts areadapted to be operatively engaged to allow articulating motion betweensaid first and second parts.
 21. An intervertebral implant according toclaim 18, wherein the first and second outer surfaces comprise a roughcoating.
 22. An intervertebral implant according to claim 18, whereinthe second part comprises two pieces, including a first piece thatincludes the second anchor and a pivot insert second piece that includessaid convex portion.
 23. An intervertebral implant according to claim18, wherein the overall length of both the first and second anchors isgreater than one half of the overall length of the respective midline.24. An intervertebral implant according to claim 18, wherein each of thefirst and second anchors is a single uninterrupted solid piece.
 25. Anintervertebral implant according to claim 18, wherein each of the firstand second anchors comprises a series of teeth.
 26. An intervertebralimplant according to claim 18, wherein both of the first and secondanchors includes an outward edge, wherein said outward edge liesessentially on a straight line.
 27. An intervertebral implant accordingto claim 18, wherein the first outer surface and the second outersurface include at least one protrusion oriented outwardly therefromwith a height substantially less than the height of the respective firstor second anchor on the same outer surface as the at least oneprotrusion.
 28. An intervertebral implant configured to be inserted intoan intervertebral space between adjacent first and second vertebrae,comprising: a first part having a substantially flat first outer surfaceadapted for engaging the first vertebra and an opposite-facing innersurface that includes a concave portion, and a first sidewall locatedbetween the first outer and inner surfaces extending around thecircumference of the first part; a second part having a substantiallyflat second outer surface adapted for engaging the second vertebra, andan opposite-facing inner surface having a convex portion adapted tooperatively engage the concave portion of the first part, and a secondsidewall located between the second outer and inner surfaces extendingaround the circumference of the second part, wherein on the second innersurface, located between the convex portion and the second sidewall andlocated radially outward of the convex portion, there is a portion notadapted to engage the concave portion of the first part; wherein atleast one of the first part concave portion and the second part convexportion is a spherical surface; wherein the first part and the secondpart have a leading end and a trailing end opposite the leading end, andopposing lateral sides between the leading end and the trailing end;wherein the first and second parts each have first and second midlinesextending in the direction from the trailing end to the leading end onthe first and second outer surfaces, respectively, the first and secondmidlines passing essentially through the center, between the lateralsides, of the first and second outer surfaces, respectively; a firstanchor extending outwardly from the first outer surface, wherein saidfirst anchor is elongated along and straddles said first midline; and asecond anchor extending outwardly from the second outer surface, whereinsaid second anchor is elongated along and straddles said second midline;wherein the first and second parts can be engaged in an insertionposition with the respective leading ends forward and the lateral sidesof the first part generally parallel with the lateral sides of thesecond part such that the elongated anchors lie in essentially the samevertical plane; wherein each of the first and second anchors has aheight greater than its width, and wherein the implant is adapted to beconfigured in the insertion position with the elongated anchorsvertically oriented in the direction of the respective anchor height,the first sidewall is located in a different horizontal plane than thesecond sidewall.
 29. An intervertebral implant according to claim 28,wherein the first and second parts are, in plan view, generallyrectangular in shape.
 30. An intervertebral implant according to claim28, wherein each of the first and second anchors is adapted to beanchored in a groove in the respective first or second vertebra.
 31. Anintervertebral implant according to claim 30, wherein the first andsecond parts are adapted for assembly such that the first and secondanchors are essentially coplanar and vertically aligned with each other.32. An intervertebral implant according to claim 30, wherein the firstand second parts are adapted to be operatively engaged to allowpivotability of said first part relative to said second part.
 33. Anintervertebral implant according to claim 30, wherein the first andsecond parts are adapted to be operatively engaged to allow articulatingmotion between said first and second parts.
 34. An intervertebralimplant according to claim 30, wherein the first and second outersurfaces comprise a rough coating.
 35. An intervertebral implantaccording to claim 30, wherein the second part comprises two pieces,including a first piece which includes the second anchor and a pivotinsert second piece which includes said convex portion.
 36. Anintervertebral implant according to claim 30, wherein the height of thefirst anchor is greater than a height of a remainder of its respectivefirst or second part.
 37. An intervertebral implant according to claim30, wherein the overall length of each anchor is greater than one halfof the overall length of the respective midline of the respective outersurface.
 38. An intervertebral implant according to claim 30, whereineach of the first and second anchors is a single uninterrupted solidpiece extending outwardly from one of the first and second outersurfaces, respectively.
 39. An intervertebral implant according to claim30, wherein each of the first and second anchors comprises a series ofteeth.
 40. An intervertebral implant according to claim 30, wherein thefirst and second outer surfaces further comprise at least one protrusionoriented outwardly from the respective outer surface with a heightsubstantially less than the height of the anchor on the respective outersurface.